Closing device in an injection moulding machine for synthetic materials

ABSTRACT

The invention relates to a clamping device for an injection molding machine for plastics, including a fixed platen ( 11 ) which is connected to a moving platen ( 12 ) by means of a toggle mechanism ( 13 ). A hollow-shaft motor ( 7 ) is provided to cooperate with a spindle ( 21 ) for operating the toggle mechanism, wherein the hollow-shaft motor ( 7 ) is connected to the toggle mechanism ( 13 ). According to the invention, the spindle ( 21 ) is arranged in a rotationally fixed manner, the end of the spindle ( 21 ), facing the moving platen ( 12 ), is in engagement with the rotor ( 6 ) of the hollow-shaft motor ( 7 ), and the stator ( 4 ) of the hollow-shaft motor is connected with the toggle mechanism ( 13 ). Preferably, a spindle nut is fixed in the rotor ( 6 ) for engagement with the spindle ( 21 ), preferably in the form of a recirculating ball screw.

[0001] The invention relates to a clamping device according to the preamble of claim 1.

[0002] EP 0658 136 B1 discloses a clamping unit for molding tools of injection molding machines, including a clamping system in the form of a toggle mechanism, disposed between the moving platen and an end platen, for displacing the moving platen. Several so-called five-point toggle lever systems are coupled with a common crosshead. A threaded spindle is connected in fixed rotative engagement upon the crosshead and engages a nut which is immobile in axial direction but received in the end platen for rotation. The rotary drive is implemented by coupling the nut to a hollow shaft of an electric motor which is flange-mounted to the outside of the end platen. The hollow shaft is internally so dimensioned as to be suitable to easily receive the entire length of the threaded spindle, when the threaded spindle extends rearwards out of the nut. The toggle lever systems are in symmetric relationship to the force axis of the clamping unit, and the threaded spindle, the spindle nut and the electric motor with its hollow shaft are in alignment with the force axis of the clamping unit. A similar system is described in DE-PS 195 24 314 C1.

[0003] These systems have shortcomings relating to a comparably long construction of the clamping device because the electric motor is arranged outside the end platen and the inner dimension of the hollow shaft is suited to the spindle length.

[0004] Generic U.S. Pat. No. 5,804,224 discloses (see FIG. 1) the secure ment of the hollow-shaft motor to the crosshead of the toggle type clamping unit and to drive with the rotor a spindle which is in engagement with a spindle nut that is non-rotatably fixed on the backside of the end platen. As the rotor is rotated, the spindle is caused to rotate and the unit of spindle and hollow-shaft motor is moved axially to the rear and the front, as a consequence of the engagement with the fixed spindle nut, so that the toggle mechanism is operated. This embodiment has also the drawback that the clamping device demands a relative large space because the spindle juts out considerably from the backside of the end platen, when the clamping unit is open.

[0005] The invention is based on the object to provide a clamping device of this type, which has a significantly shorter length while still allowing a cost-efficient construction.

[0006] This object is realized in accordance with the invention by the features of claim 1. The subsequent claims are advantageous improvements of the invention.

[0007] In accordance with the invention, the spindle is arranged in a rotationally fixed manner and the spindle end facing the moving platen is in engagement with the rotor, i.e. the hollow shaft, of the hollow-shaft motor, while the stator of the hollow-shaft motor is connected with the toggle mechanism. The spindle can be secured in the end platen or in an anchor plate arranged therebehind. When an end platen with opening is used, the anchor plate enables the hollow-shaft motor to plunge into the end platen, thereby further reducing the demand for space. Moreover, the thickness and the shape of the end platen can be randomly configured in this manner and suited to the respective requirements. The hollow-shaft motor is either flange-mounted directly onto the crosshead or integrated therein, for example, by providing the crosshead with a recess for receiving the hollow-shaft motor. As an alternative, the stator may also be coupled directly to the toggle mechanism via suitable connecting elements. As a consequence of the invention, the reaction moment of the drive and the guidance of the cross head can be realized by a single cost-efficient construction.

[0008] An example of the invention is illustrated in the attached FIG. 1. Arranged on a machine bed 16 is a fixed platen 11, whereby a moveable platen 12 is able to move axially relative to the fixed platen by a toggle mechanism 13. The fixed platen 11 is connected via the machine bed 16 with an end platen 19. A spindle 21 is guided with its end distal to the moving platen through the end platen 19 and connected in a rotationally fixed manner in an anchor plate 3. Flange-mounted to the toggle mechanism 13 on the other end of the spindle 21 is a hollow-shaft motor 7. A spindle nut 5 is coupled with the hollow shaft or the rotor 6 of the hollow-shaft motor and is in engagement with the spindle 21. In the presently illustrated example, the stator 4 of the hollow-shaft motor is flange-mounted directly to the toggle mechanism 13. The hollow-shaft motor 7 may also be received in its entirety by the crosshead of the toggle mechanism, when the latter has a recess suited to the hollow-shaft motor. In this way, the functions of the crosshead and those of the drive motor are united.

[0009] Optionally, in particular when heavy hollow-shaft motors are involved, it is advantageous to provide carrier arms 23 laterally and/or underneath the hollow-shaft motor for movable support of the hollow-shaft motor 7. In this way, the spindle 21 and the joints of the toggle mechanism are relieved. The carrier arms 23 may be secured in the end platen 19 or extend through the end platen and fixed in the anchor plate 3 situated therebehind. In FIG. 1, only the rear one of the two lateral carrier arms 23 is partially visible.

Portion List

[0010] Injection Molding Machine

[0011]3 anchor plate

[0012]11 fixed platen

[0013]12 moving platen

[0014]13 toggle mechanism

[0015]16 machine bed

[0016]19 end platen

[0017] Drive

[0018]4 stator of the hollow-shaft motor

[0019]5 spindle nut

[0020]6 rotor of the hollow-shaft motor

[0021]7 hollow-shaft motor

[0022]21 spindle

[0023]23 rear carrier arm

[0024]24 balls 

1. Clamping device for an injection molding machine for plastics, comprising a fixed paten, which is connected via a toggle mechanism with a moving platen, wherein a hollow-shaft motor interacts with a spindle for operating the toggle mechanism, and wherein the hollow-shaft motor is connected with the toggle nechanism, characterized in that the spindle (21) is arranged in rotationally fixed manner, that the end of the spindle (21), facing the moving platen (12), is in engagement with the rotor (6) of the hollow-shaft motor (7), and that the stator (4) of the hollow-shaft motor is connected with the toggle mechanism (13).
 2. Clamping device according to claim 1, characterized in that the rotor (6) has an internal thread which meshes with the thread of the spindle (21), preferably via balls (24).
 3. Clamping device according to claim 1, characterized in that a spindle nut (5) is secured in the rotor (6) for engagement with the spindle (21), preferably via balls (24).
 4. Clamping device according to one of the claims 1 to 3, characterized in that the toggle mechanism is coupled to a crosshead, and that the hollow-shaft motor is flange-mounted to the crosshead.
 5. Clamping device according to one of the claims 1 to 3, characterized in that the toggle mechanism is coupled to a crosshead, and that the crosshead has a recess for receiving the hollow-shaft motor.
 6. Clamping device according to one of the claims 1 to 3, characterized in that the toggle mechanism is coupled directly to the stator of the hollow-shaft motor.
 7. Clamping device according to claim 6, characterized in that the stator of the hollow-shaft motor is movably supported on carrier arms (23) which are arranged laterally to and/or underneath the hollow-shaft motor (7).
 8. Clamping device according to one of the claims 1 to 7, characterized in that the moving platen (12) is movably guided on several tie bars, and that one or more of these tie bars serve at the same time as carrier arm (23) for the hollow-shaft motor itself or the stator (4) of the hollow-shaft motor.
 9. Clamping device according to one of the claims 1 to 8, characterized in that the spindle (21) is guided through an end platen (19) and secured in a rotationally fixed manner in an anchor plate (3). 